use x86_64::structures::gdt::{Descriptor, GlobalDescriptorTable, SegmentSelector};
use x86_64::structures::tss::TaskStateSegment;
use x86_64::VirtAddr;

use lazy_static::lazy_static;

pub fn init() {
    GDT.0.load();

    use x86_64::instructions::segmentation::set_cs;
    use x86_64::instructions::tables::load_tss;
    unsafe {
        set_cs(GDT.1.code_selector);
        load_tss(GDT.1.tss_selector);
    }
}

lazy_static! {
    static ref GDT:(GlobalDescriptorTable,Selectors)={
        let mut gdt=GlobalDescriptorTable::new();
        let code_selector=gdt.add_entry(Descriptor::kernel_code_segment());
        let tss_selector=gdt.add_entry(Descriptor::tss_segment(&TSS));
        (gdt,Selectors{code_selector,tss_selector})
    };
}

struct Selectors {
    code_selector: SegmentSelector,
    tss_selector: SegmentSelector,
}

pub const DOUBLE_FAULT_IST_INDEX: u16 = 0;
lazy_static! {
    static ref TSS:TaskStateSegment={
        let mut tss=TaskStateSegment::new();
        tss.interrupt_stack_table[DOUBLE_FAULT_IST_INDEX as usize]={
            const STACK_SIZE:usize=4096;
            static mut STACK:[u8;STACK_SIZE]=[0;STACK_SIZE];

            let stack_start=VirtAddr::from_ptr(unsafe{&STACK});
            let stack_end=stack_start+STACK_SIZE;
            stack_end
        };
        tss
    };
}
